Add example for custom script

[cmaumet]

As discussed with @dorahermes in Copenhagen BIDS_derivatives meeting, we should add examples/recipes on how to implement BIDS-Prov to represent
→ custom scripts.

[cmaumet]

This is currently in-progress by @bclenet , ideally should be its own example in BIDS-examples

[bclenet]

The [BEP028] provenance - SPM preprocessing example shows provenance metadata for a functional MRI preprocessing performed with SPM. In this example, each line of a custom matlabbatch script (the code/spm_preprocessing.m file in the example) is described as an activity provenance object.

@cmaumet @dorahermes Would that answer the issue or do you have something else in mind ?

Otherwise I can create other examples for different usecases, such as:

• describing the whole custom script as one activity (this would be relevant e.g. for dataset level provenance description).
• a custom script implementing a pipeline with a workflow manager (e.g. nipype)